1. Field of the Invention
The present invention relates generally to methods of manufacturing ultrapure water, and more specifically, to a method of manufacturing ultrapure water so improved that an organic substance having a boiling point lower than water does not remain. The invention further relates to an apparatus for manufacturing such ultrapure water.
2. Description of the Background Art
In recent years, for ultrapure water for use in the field of electronics or medication, water with a higher purity is in demand with technological development in the field. Particularly for water for washing semiconductor wafers, water with an even higher purity than conventional ultrapure water, in other words water including few constituents other than water is required as the integration density of integrated circuits increases.
FIG. 8 is a view showing the concept of a ultrapure water manufacturing apparatus utilizing distillation, which has been conventionally utilized. The conventional pure water manufacturing apparatus includes an evaporation container 2 for accommodating primary water to be treated and evaporating the water. Evaporation container 2 is provided on a heater 3. A cooler 4 is provided on evaporation container 2. A distilled water inlet tube 5 is connected to cooler 4. Evaporation container 2 is provided with a water to be treated (raw water) injection tube 1 for supplying raw water, in other words for supplying primary water to be treated into the evaporation container. The primary water means water produced by condensing and filtering industrial water and then passing the resultant water through ion-exchange resin. The primary water includes organic substances, non-organic substances, charged fine particles, impurities such as alcohol or the like, e.g. methanol, ethanol, butanol, and octanol.
Such an apparatus used to use silica glass for its part in contact with liquid (water to be treated) conventionally, but use of silica glass is disadvantageous, because silica will be contained in distilled water. Therefore, all the part in contact with liquid is formed of stainless steel. Further, recently, an apparatus is utilized in which its part of stainless steel is polished in an electrolytic manner to increase its specific resistance to 18M.OMEGA..multidot.cm, in order to restrict impurities such as metallic ions from dissolving.
Now, an operation will be described. Raw water to be treated is introduced into evaporation container 2 through water injection tube 1. The crude water introduced into evaporation container 2 is heated by heater 3 to boil. Evaporated water is cooled in cooler 4 to be distilled water, and evacuated externally through a ultrapure water supply tube 5 and led to a use point.
The conventional ultrapure water manufacturing apparatus utilizing distillation having the structure described above can remove non-volatile impurities such as silica and volatile impurities having a boiling point higher than water.
However, it can not remove volatile impurities having a boiling point lower than water and is encountered with a disadvantage that organic substances having a low boiling point remain in the produced ultrapure water.